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Internet Applications Chapter 7 Database Management Systems 3ed, R. Ramakrishnan and J. Gehrke 1 Uniform Resource Identifiers Uniform naming schema to identify resources on the Internet A resource can be anything: Index.html mysong.mp3 picture.jpg Example URIs: http://www.cs.wisc.edu/~dbbook/index.html mailto:[email protected] Database Management Systems 3ed, R. Ramakrishnan and J. Gehrke 2 Structure of URIs http://www.cs.wisc.edu/~dbbook/index.html URI has three parts: Naming schema (http) Name of the host computer (www.cs.wisc.edu) Name of the resource (~dbbook/index.html) URLs are a subset of URIs Database Management Systems 3ed, R. Ramakrishnan and J. Gehrke 3 Hypertext Transfer Protocol What is a communication protocol? Set of standards that defines the structure of messages Examples: TCP, IP, HTTP What happens if you click on www.cs.wisc.edu/~dbbook/index.html? Client (web browser) sends HTTP request to server Server receives request and replies Client receives reply; makes new requests Database Management Systems 3ed, R. Ramakrishnan and J. Gehrke 4 HTTP (Contd.) Client to Server: Server replies: GET ~/index.html HTTP/1.1 User-agent: Mozilla/4.0 Accept: text/html, image/gif, image/jpeg HTTP/1.1 200 OK Date: Mon, 04 Mar 2002 12:00:00 GMT Server: Apache/1.3.0 (Linux) Last-Modified: Mon, 01 Mar 2002 09:23:24 GMT Content-Length: 1024 Content-Type: text/html <HTML> <HEAD></HEAD> <BODY> <h1>Barns and Nobble Internet Bookstore</h1> Our inventory: <h3>Science</h3> <b>The Character of Physical Law</b> ... Database Management Systems 3ed, R. Ramakrishnan and J. Gehrke 5 HTTP Protocol Structure HTTP Requests Request line: GET ~/index.html HTTP/1.1 GET: Http method field (possible values are GET and POST) ~/index.html: URI field HTTP/1.1: HTTP version field Type of client: User-agent: Mozilla/4.0 What types of files will the client accept: Accept: text/html, image/gif, image/jpeg Database Management Systems 3ed, R. Ramakrishnan and J. Gehrke 6 HTTP Protocol Structure (Contd.) HTTP Responses Status line: HTTP/1.1 200 OK HTTP version: HTTP/1.1 Status code: 200 Server message: OK Common status code/server message combinations: • • • • 200 OK: Request succeeded 400 Bad Request: Request could not be fulfilled by the server 404 Not Found: Requested object does not exist on the server 505 HTTP Version not Supported Date when the object was created: Last-Modified: Mon, 01 Mar 2002 09:23:24 GMT Number of bytes being sent: Content-Length: 1024 What type is the object being sent: Content-Type: text/html Other information such as the server type, server time, etc. Database Management Systems 3ed, R. Ramakrishnan and J. Gehrke 7 Some Remarks About HTTP HTTP is stateless No “sessions” Every message is completely self-contained No previous interaction is “remembered” by the protocol Tradeoff between ease of implementation and ease of application development: Other functionality has to be built on top Implications for applications: Any state information (shopping carts, user login-information) need to be encoded in every HTTP request and response! Popular methods on how to maintain state: • Cookies • Dynamically generate unique URL’s at the server level Database Management Systems 3ed, R. Ramakrishnan and J. Gehrke 8 Web Data Formats HTML The presentation language for the Internet XML A self-describing, hierarchal data model DTD Standardizing schemas for XML XSLT RDF OWL Database Management Systems 3ed, R. Ramakrishnan and J. Gehrke 9 HTML: An Example <HTML> <HEAD></HEAD> <BODY> <h1>Barns and Nobble Internet Bookstore</h1> Our inventory: <h3>Science</h3> <b>The Character of Physical Law</b> <UL> <LI>Author: Richard Feynman</LI> <LI>Published 1980</LI> <LI>Hardcover</LI> </UL> <h3>Fiction</h3> <b>Waiting for the Mahatma</b> <UL> <LI>Author: R.K. Narayan</LI> <LI>Published 1981</LI> </UL> <b>The English Teacher</b> <UL> <LI>Author: R.K. Narayan</LI> <LI>Published 1980</LI> <LI>Paperback</LI> </UL> </BODY> </HTML> Database Management Systems 3ed, R. Ramakrishnan and J. Gehrke 10 HTML: A Short Introduction HTML is a markup language Commands are tags: Start tag and end tag Examples: • <HTML> … </HTML> • <UL> … </UL> Many editors automatically generate HTML directly from your document (e.g., Microsoft Word has an “Save as html” facility) Database Management Systems 3ed, R. Ramakrishnan and J. Gehrke 11 HTML: Sample Commands <HTML>: <UL>: unordered list <LI>: list entry <h1>: largest heading <h2>: second-level heading, <h3>, <h4> analogous <B>Title</B>: Bold Database Management Systems 3ed, R. Ramakrishnan and J. Gehrke 12 XML – What is this? Science Hardcover Richard Feynman The Character of Physical Law 1980 Fiction R.K. Narayan Waiting for the Mahatma 1981 Fiction R.K. Narayan The English Teacher 1980 Database Management Systems 3ed, R. Ramakrishnan and J. Gehrke 13 XML: An Example <?xml version="1.0" encoding="UTF-8" standalone="yes"?> <BOOKLIST> <BOOK genre="Science" format="Hardcover"> <AUTHOR> <FIRSTNAME>Richard</FIRSTNAME><LASTNAME>Feynman</LASTNAME> </AUTHOR> <TITLE>The Character of Physical Law</TITLE> <PUBLISHED>1980</PUBLISHED> </BOOK> <BOOK genre="Fiction"> <AUTHOR> <FIRSTNAME>R.K.</FIRSTNAME><LASTNAME>Narayan</LASTNAME> </AUTHOR> <TITLE>Waiting for the Mahatma</TITLE> <PUBLISHED>1981</PUBLISHED> </BOOK> <BOOK genre="Fiction"> <AUTHOR> <FIRSTNAME>R.K.</FIRSTNAME><LASTNAME>Narayan</LASTNAME> </AUTHOR> <TITLE>The English Teacher</TITLE> <PUBLISHED>1980</PUBLISHED> </BOOK> </BOOKLIST> Database Management Systems 3ed, R. Ramakrishnan and J. Gehrke 14 XML – The Extensible Markup Language Language A way of communicating information Markup Notes or meta-data that describe your data or language Extensible Limitless ability to define new languages or data sets Database Management Systems 3ed, R. Ramakrishnan and J. Gehrke 15 XML – What’s The Point? You can include your data and a description of what the data represents This is useful for defining your own language or protocol Example: Chemical Markup Language <molecule> <weight>234.5</weight> <Spectra>…</Spectra> <Figures>…</Figures> </molecule> XML design goals: XML should be compatible with SGML It should be easy to write XML processors The design should be formal and precise Database Management Systems 3ed, R. Ramakrishnan and J. Gehrke 16 DTD – Document Type Definition A DTD is a schema for Xml data Xml protocols and languages can be standardized with DTD files A DTD says what elements and attributes are required or optional Defines the formal structure of the language Database Management Systems 3ed, R. Ramakrishnan and J. Gehrke 17 DTD – An Example <?xml version='1.0'?> <!ELEMENT Basket (Cherry+, (Apple | Orange)*) > <!ELEMENT Cherry EMPTY> <!ATTLIST Cherry flavor CDATA #REQUIRED> <!ELEMENT Apple EMPTY> <!ATTLIST Apple color CDATA #REQUIRED> <!ELEMENT Orange EMPTY> <!ATTLIST Orange location ‘Florida’> -------------------------------------------------------------------------------- <Basket> <Cherry flavor=‘good’/> <Apple color=‘red’/> <Apple color=‘green’/> </Basket> <Basket> <Apple/> <Cherry flavor=‘good’/> <Orange/> </Basket> Database Management Systems 3ed, R. Ramakrishnan and J. Gehrke 18 XML and DTDs More and more standardized DTDs will be developed MathML Chemical Markup Language Allows light-weight exchange of data with the same semantics Sophisticated query languages for XML are available: Xquery XPath Database Management Systems 3ed, R. Ramakrishnan and J. Gehrke 19 Components of Data-Intensive Systems Three separate types of functionality: Data management Application logic Presentation The system architecture determines whether these three components reside on a single system (“tier“) or are distributed across several tiers Database Management Systems 3ed, R. Ramakrishnan and J. Gehrke 20 The Three-Tier Architecture Presentation tier Middle tier Data management tier Client Program (Web Browser) Application Server Database System Database Management Systems 3ed, R. Ramakrishnan and J. Gehrke 21 The Three Layers Presentation tier Primary interface to the user Needs to adapt to different display devices (PC, PDA, cell phone, voice access?) Middle tier Implements business logic (implements complex actions, maintains state between different steps of a workflow) Accesses different data management systems Data management tier One or more standard database management systems Database Management Systems 3ed, R. Ramakrishnan and J. Gehrke 22 Example 1: Airline reservations Build a system for making airline reservations What is done in the different tiers? Database System Airline info, available seats, customer info, etc. Application Server Logic to make reservations, cancel reservations, add new airlines, etc. Client Program Log in different users, display forms and humanreadable output Database Management Systems 3ed, R. Ramakrishnan and J. Gehrke 23 Example 2: Course Enrollment Build a system using which students can enroll in courses Database System Student info, course info, instructor info, course availability, pre-requisites, etc. Application Server Logic to add a course, drop a course, create a new course, etc. Client Program Log in different users (students, staff, faculty), display forms and human-readable output Database Management Systems 3ed, R. Ramakrishnan and J. Gehrke 24 Technologies Client Program (Web Browser) Application Server (Apache Tomcat, J2EE) Database System (Oracle,DB2,SQL Server) Database Management Systems 3ed, R. Ramakrishnan and J. Gehrke HTML Javascript XSLT JavaFX Flex, etc. JSP Servlets Cookies CGI XML Stored Procedures 25 Application Servers Idea: Avoid the overhead of CGI Main pool of threads of processes Manage connections Enable access to heterogeneous data sources Other functionality such as APIs for session management Database Management Systems 3ed, R. Ramakrishnan and J. Gehrke 26 Application Server: Process Structure Process Structure Web Browser HTTP Web Server C++ Application JavaBeans Application Server JDBC ODBC DBMS 1 DBMS 2 Pool of Servlets Database Management Systems 3ed, R. Ramakrishnan and J. Gehrke 27
